Zopolrestat is a potent, reversible, noncompetitive inhibitor of aldose reductase, the first enzyme in the polyol pathway. Substantial evidence exists to suggest that increased flux of glucose through the polyol pathway may play an important role in the pathogenesis of the long-term complications of diabetes, particularly neuropathy. This study looks to determine the safety and efficacy of long-term administration of zopolrestat in subjects with diabetic peripheral symmetrical polyneuropathy.